Variable pitch propeller



July 18, 1950 L. K. MILLER VARIABLE PITCH PROPELLER 2 Sheets-Sheet 1Filed Aug. 6, 1945 l INVENTOR lam; ffiMu 5/? BY a ya Z ATTORzYs i/' 1950L. K. MILLER 2,515,607

I VARIABLE PITCH PROPELLER Filed Aug. 6, 1945 2 Sheets-Sheet 2 20 T {I H23 w s /7 JZZQQ.

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INVENTOR .Zo AL 111/2215? 4 .q 4 g BY ATTORBZYS Patented July 18, 1950UNITED STATES PATENT. OFFICE f .lasiacm "VARIABLE PITCHPROPELLER LoyalK. Miller, Lawrence, Kans. Application August a, 1945, Serial No.609,051

- This invention relates to improvements in airplane propellers whichare automatically adjustable in pitch to accommodate the varyingconditions arising for example during take-off and cruising. Whilenumerous proposals have been made as to the design of'such-automaticvariable pitch propellers, they have been intrinsically complex andexpensive, and none has been suitable for use on small planes. It is oneobject of the invention to produce a simple and effective mechanism forautomatically varying the pitch of apropeller. It is a further object toprovide such a propeller in which theweight. of the controllingmechanism will be concentrated near the hub and in which tendency tovibration will be lessened. A further object is to providesuch apropeller in which dangerous conditions due to breakage of thecontrolling elements will be minimized. A further object is to providesuch a propeller in which the operating mechanism will not be subjectedto forces tending to cause it to bind or wear. A further object is toprovide a design in which standard propeller blades may be used.

The invention will now be described with refs erence to the accompanyingdrawings, inwhich Fig. 1 is a plan view, partly broken away, of thepropeller hub showing the preferred manner of mounting the blades; l

.Fig. 2is a section on line 22 of Fig. 1-;

cFig. 3 is a section on line 3-3 of Fig. 1;

Fig. 4 is a section on line 44 of Fig. 1;

Fig. 5 is a detail of a rotation limiting member carried by the shank ofthe propeller;

' Fig. 6 is a detail of a sleeve in which the shank of the propeller isfixed;

Fig. '7 is a detail showing the propeller mounting in the positionassumed when the plane is at rest or cruising;

. Fig. 8 is a similar view showing the position assumed during take-off;a

Fig. 9 is a detail, similarto a portion of Fig. 1 showing amodification;

Fig 10 is a similar view showing the take-off position;

Fig. 11 is a. section on line Il-ll of Fig. 9;

and i Fig. 12 is a section on line l2-l2 of Fig. 9.

The huh I is secured to the propeller shaft 2 in any desired way, as bya nut 3 and" cotter 3 Claims. (Cl. 170-160.11)

pin 4. a The hub has several shouldered portions 5, there being one suchportion for each blade of the propeller. To each shouldered portion issecured as by screws 6 a casing I having an inturned flange 8. Anannular fixed abutment or thrust member 9 is fastened as by screws Illto the inside of this flange and serves to resist and limit outwardmotion of the propeller blade H in amanner to be described. The shank I2of the blade fits snugly within a sleeve l3 to which itis secured firmlyin any suitable way as by pins Id. The inner end of the sleeve [3 has anoutwardly extending flange [5 bearing against the inner wall of thecasing I with a sliding fit. A movable abutment l6, formed separatelyfrom the sleeve for .convenience in manufacturing and assembling butfunctionally integral with it and with the propeller blade, is securedas by screws 11 to the outer face of the flange. This movable abutmenthas a lug l8 movable both axially and rotatably in a notch IS in theshouldered portion 5 of the hub, thenotch having a sufficientcircumferential extent to permit only the desired amount of rotativemovement of the propeller blade. Other forms of limit stops mayobviously be substituted if desired. A limit to the outward movement ofthe blade is secured by contact of the flange IS with a tubularextension 20 of the fixed abutment 9. This prevents serious unbalance incase of breakage of theoontrollin means now to be described.

The rotative movement of the blade is controlled by a circumferentialseries of rod-like springs 2|, here shown as circular in cross-section,secured both-to the movable and fixed abutments. The connection to oneof the abutments, here shown as the fixed abutment 9, may besubstantially rigid, while the connection to the other abutmentpreferably has some degree of freedom to avoid unduestress in thespring. Holes 22 in the fixed abutment are shown as receiving one end ofthe springs, both the holes and the springs being arranged at an angleso that the springs are given a generally helical position. At the otherend the springs are bent so as to pass into slightly oversized holes 23in the outwardly extending flange [5 of sleeve I3, these holes beinggenerally parallel to the axis of th: bladeand being closed by thethrust membe! I In the position of the parts assumed when the propellershaft is not rotating or when the plane is cruising, the springs arepreferably preloaded with a substantial initial strain. This can be doneon assembly, and is for the purpose of preventing any change in pitch ofthe propeller until a predetermined threshold speed has been reached. Asshown in Fig. '7, the end of each spring bears against the side of thehole in which it is placed, and being under strain holds the propellerin such angular position that the lug I8 is against one side of thenotch. This keeps the propeller at maximum pitch, as is suitable forcruising.

As the engine is speeded up at take-off the centrifugalforce on theblades increases, and each sleeve i3 is given a tendency to moveoutwardly through the fixed abutment 9. This is resisted by thecircumferential series of spring rods, and until the centrifugal forcebecomes great enough to overcome the preloaded strain given to thesprings on assembly no turning of the blade can occur. When the enginespeed is enough so that the centrifugal force on the blades can overcomethe preloading of the springs (preferably a speed slightly abovecruisingspeedlthe springs will be flexed-as indicated in Fig. 8 and bythe dotted lines for one of the springs at 2! in Fig. 1. Since thesprings are set at an angle this flexing will force the flange IE torotate in such a direction as to decrease the pitch of the blade, or inother words to cause the blade to turn in its socket so as to lie morenearly in the plane in which the blade travels. This turning is assistedby the air forces acting :on the blade. ance of the propeller torotating and allows the engine to pick up speed further and thus toincrease the power delivered. A minimum pitchis, however, maintained atall times by the limited movement allowed to the lug [8 in the notch 19.

After the take-elf, during which maximum power is desired,'the throttleis partially closed and the engine speed thus reduced. The decreased"centrifugal force on the blades will drop to a degree insufiicientto-resist the restoring action of the springs, and the pitcher thepropeller will be held at a point determined by and-equilibrium betweenthe centrifugal force and the restoring action of the partially unbentsprings. Generally the preloaded tension of the springs will be soadjusted that when the engine speed is reduced to the cruising range theblades will be returned to the position of maximumpitch shown in Figs. 1and '7.

It was stated above that the holes 23are prefer ably larger than theends of the springs. The purpose of this is to allow thesprings toflex-gradually and not have a localized flex point, asmight occur werethe springs tightly held at bothends. While this construction is ingeneral preferred, the springs may if desiredbe mounted soas to beeither tight or loose at both ends. Where the loose mounting is used theends of the springs are preferably bent as shown" inFigs. '7 and 8 sothat they extend generally in the direction of the axis of the propellerblade and always engage-one side of the hole. A slight tilt is given tothe springs as the pitch ischanged, but by having the spring engage thehole squarely in the position of minimum pitch (Fig.8) cutting of. thespring under its condition of maximum, stress by the corner of the holewill be avoided. The'construce tion of the abutment 16 as separate fromthe flange i is of use in avoiding difiicultyiin making holes 23 all ofuniform depth, as is desirablein Decreasing'the pitch reduces the'resistorder to have the centrifugal force borne equally by all thesprings of the set. In this way the holes can be bored all the waythrough the flange, and when the abutment is screwed in place it forms acommon bottom for the holes which lie in a single plane. By grinding offthe free ends of the springs after the opposite ends have been mountedin the fixed abutment 9 uniform distribution of pressure to the severalsprings by the trust member [6 will be insured. Preloading of thesprings can also be secured by this construction since the springs willbe flexed as the screws H are tightened.

Figs. 9 to 12 show an alternative construction in which flat rodsprings'areused. Since all parts are the" same except for the springsand their mounting the other parts will not be redescribed. In this casethe fiat springs 24 are set in slanting notches 25 milled in the fixedabutment 9, being retained within the notches by the casing I. At theother end the springs are set into preferably oversized notches 2G inthe flange 15, being retained by'the casing and by the movable abutmentl6. Since the flat springs are arranged on an angle the two sets ofnotches are set at oppositely inclined anglesgasshow inFigsl l1 and 12to minimize .the tendency to pull out -of the notches as the springsflex =Thexoperati0r1 is the same as in the first form. 1

Iclaim:

- 1. A variable pitch-propellerhaving ahub, a casing on the hub for each"blade, each casingreceiving the shank of ithe propeller; blade, eachcasing being-formed of a cylindrical body withan inturned outerendasleeve secured to the "shank of the blade =and =extending withinthe'casing, an annular thrust-member' carriedby the casingandsurrounding the-sleeve and having sliding engage.- ment therewith, asecond thrust gmembercarried by the sleeve within the casing, acircumferential series of rod-like springs extending on .an anglebetween the two thrust members, thejspri-ngs being fixed at one endtoone thrust member and being received. loosely holes; in the :secondthrustmember, the springs being inclined: around the axis ofthebladeinthe same direction as that in which the edges of the'blade aredispl'aced from a plane passing through ,wtheaxis or .the blade :atright angles to the axis of rotationofthe pro-. peller.

,2. A variable pitch :propellerxcomprising ahub provided with radiallydirected: housings one'for the shank 'of each rpropeller'blzidey-aspring ree ceiving abutment carried by'eachlhou'sing, 'a-springreceiving abutment carried by- 'the inner end of theshank of eachpropellerbl'a'de, at least one of said spring receiving abutments beingcomposed of a collar to receive "the axialthrust of a series of rodsprings and an adjacent 'collariiavinge series of holes to receiveandLposition the springs, said holes being sufficiently larger than thesprings to permit the flatter to bear against on'eside' of the holewithout binding, and a. circumferential series of rod-like springspositionedz'around the shank in :generally helical :formation, the:springs being inclined around thefa-xis {of the bladein the samedirectionas that in which the edges of the blade are displaced froma-plane'passing through the axis of Ethe fblade at right anglestotheaxis of rotation of the propeller. H 3. A variable pitchpropellercomprising a=hub with radially directed housings one for the shanlc; ofeach propeller blade, a;springreceiving abutment carried byeach;housing, a second spring ceiv a utment qe riedbx teeii n r endis i;

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Number Name Date Kelm Apr. 3, 1934 GilbertSept. 24, 1940 Fraser Oct. 29, 1940 Hackethal Mar. 5, 1946 FOREIGNPATENTS Country Date Switzerland Apr. 15, 1937

